sig_analog: Add fuller Caller ID support.

A previous change, ASTERISK_29991, made it possible
to send additional Caller ID parameters that were
not previously supported.

This change adds support for analog DAHDI channels
to now be able to receive these parameters for
on-hook Caller ID, in order to enhance the usability
of CPE that support these parameters.

Resolves: #94
ASTERISK-30331

UserNote: Additional Caller ID properties are now supported on
incoming calls to FXS stations, namely the
redirecting reason and call qualifier.

(cherry picked from commit f56477a604)

funcs/func_callerid.c

@@ -182,6 +182,21 @@
 					<para>Number Unavailable.</para>
 				</enum>
 			</enumlist>
+			<variablelist>
+				<variable name="CALL_QUALIFIER">
+					<para>This is a special Caller ID-related variable
+					that can be used to enable sending the Call Qualifier
+					parameter in MDMF (Multiple Data Message Format)
+					Caller ID spills.</para>
+					<para>This variable is not automatically set by Asterisk.
+					You are responsible for setting it if/when needed.</para>
+					<para>Supporting Caller ID units will display the LDC
+					(Long Distance Call) indicator when they receive this parameter.</para>
+					<para>This option must be used with a channel driver
+					that allows Asterisk to generate the Caller ID spill,
+					which currently only includes <literal>chan_dahdi</literal>.</para>
+				</variable>
+			</variablelist>
 		</description>
 	</function>
 	<function name="CONNECTEDLINE" language="en_US">